| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Takashi Osawa, Hosei University, Japan |
| Authors: | T. Osawa, Hosei University, Japan Y. Notani, Hosei University, Japan K. Hara, Hosei University, Japan K. Aoki, Hosei University, Japan K. Fujiyama, Hosei University, Japan K. Ishibashi, COMET Inc., Japan S. Suzuki, COMET Inc., Japan Y. Yamamoto, Hosei University, Japan |
| Correspondent: | Click to Email |
Cerium dioxide is one of the materials of interest as a gate stack in metal-oxide-semiconductor (MOS) devices. CeO2 is likely to crystallize, however, leading to the possible increase of the leakage current. To suppress crystallization of CeO2 thin films, Al was doped in CeO2 films during deposition using RF magnetron sputtering using CeO2 target on which Al plates were bonded with the applied RF power of 50 W at room temperature at a pressure of 5.3 Pa. The deposition was carried out with and without O2 introduction in order to investigate the influence of oxygen deficiency in the deposited film. The deposition time was adjusted so as to obtain the typical thickness of CeO2 films of 35 nm since the deposition rate decreased with increasing the O2 flow rate varying as 0, 2, 5 and 10%. The post annealing was performed in an N2 atmosphere in the temperature range from 200 to 600 °C.
The electrical properties after annealing were characterized by I-V and C-V measurements using the Hg probe as an electrode. Irrespective of the amount of O2 introduction, the leakage current at 3 MV/cm was minimized around 1.0×10-7 A/cm2 after annealing at 200 °C. After annealing at 400 °C, the leakage current increased by 3 orders of magnitude. For the sample annealed at 600 °C, the leakage current was recovered to the level of the as-deposited sample. The dielectric constant was increased with increasing amount of introduced O2. It tended to increase with increasing annealing temperature, but exceptionally decreased after annealing at 400 °C. The C-V characteristic represented the kink or even the step in the depletion region for sample annealed at 400 °C. The flat band voltage was shifted toward higher gate voltage with increasing annealing temperature, probably due to the fixed negative charge arising from Al oxides. The fact that the C-V hysteresis was broadened with the increase of introduced O2 implied that the existence of Al oxide in the film enhanced the generation of the interfacial states.
In the X-ray diffraction spectrum, the as-deposited samples represented strong CeO2 and weak Ce2O3 peaks when the amount of introduced O2 flow ratio was 0 and 2% while Ce2O3 peaks almost disappeared with the O2 introduction above 5%. After annealing at 200 – 600 °C the peak other than CeO2 was not observed. Judging from the electron diffraction image obtained from the fast Fourier transform (FFT) processing of high resolution transmission electron microscope image, CeO2 crystalline structure appeared to be destroyed due to the transition to another phase after annealing at 400 °C.